Nothing worse than a slush box puking it's guts out at an inopportune time because the owner was lax when it comes to fluid and filter changes, a mandatory and necessary evil to owning a slush-o-matic.
When they puke, the repair bill is also a wallet buster and the more complex the slush box is, the higher the repair bill is as well.
Slush boxes are entirely dependent on timely fluid and filter changes to live a long and trouble free life and something that most owners seem to not remember. Once the additives in the fluid are depleted from the heat-cool cycles and the fluid is contaminated by various wearing components inside the tranny, it's only a matter of time before it fails.
Why you never want to 'flush' a slush box, simply because 'flushing', while less expensive to perform, agitates any and all wearing components that have deposited stuff inside the tranny and flushing causes those deposits to break loose and can cause havoc with internal valving in the valve body. Something I'd never do. Always more prudent and safe to do a complete drain (including the torque convertor) and filter change and installing new, virgin fluid on the manufacturer's specified change interval which is exactly what I just did with my wife's suburban at 80K as specified in her owners manual and I had that done at the local GM dealer where she purchased the vehicle in the first place.
It's my observation the most people change their engine oil regularly but totally ignore the shush box until it fails.